Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221512 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1012 AM EST Thu Feb 22 2018 .SYNOPSIS...
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A cold front will stall to our south tonight. The front will return north as a warm front Friday. It will stall overhead Saturday. A stronger cold front will pass through from the west Sunday and high pressure will return for early next week. Saturday before a stronger cold front passes through from the west on Sunday. Low pressure may pass by to our south Monday before high pressure returns for the middle portion of next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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A cold front sags to our south from near Nelson County in west- central Virginia to just north of Richmond, Virginia. Radar across our region is relatively quiet with exception to pockets of light rain and drizzle over Grant County in West Virginia, and between Culpeper, Virginia and Annapolis, Maryland. This includes the northern and eastern suburbs of Washington, D.C. Temperatures range from the middle 40s in north-central Maryland to the middle 50s in the Virginia Piedmont and across southern Maryland. A persistent north to northeast light wind throughout the day will keep a steady flow of cooler air into our region from Pennsylvania. This cool air will undercut some slightly milder air a few thousand feet above the ground to provide a persistent cloud deck with additional periods of light rain and drizzle that will develop during the course of the remainder of the day into tonight. Aiding in this rain and drizzle development will be an upper level disturbance this afternoon. This disturbance will move off to the east tonight. Tonight`s low temperatures will range from the middle and upper 30s across most locations to perhaps the lower 40s in central Virginia. We will check local computer guidance later this morning on any changes or further possibilities of light freezing rain or freezing drizzle near the Allegheny Front in western Maryland and eastern West Virginia. Temps may dip a close to freezing... causing the chance for light freezing rain and freezing drizzle. Higher resolution guidance continues to suggest this while lower resolution guidance keeps it warmer. Did lean the forecast closer to the higher resolution guidance and also noting the dewpoints in the 20s upstream over central PA. The chance for freezing rain across these areas tonight and Friday morning are mentioned in the HWO.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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The stalled front will return north as a warm front Friday into Friday night as low pressure tracks through the Great Lakes into Canada. Latest guidance has come into decent agreement showing that the boundary makes it into the Potomac Highlands and central Shenandoah Valley. This means that most areas will be on the cool side of the boundary with max temps in the 40s to perhaps lower 50s for most areas along with plenty of clouds and times of light rain and drizzle. However...some areas in the Potomac Highlands could punch into the warm sector later Friday with temps in the 60s possible. High pressure will swing across New England Saturday into Saturday night and this will likely keep the boundary hung up over our area for Saturday as well. With the boundary overhead...certainty in the forecast is low. The boundary will separate much cooler marine air from more very warm conditions for this time of year. Latest guidance shows the boundary most likely getting hung up just south and west of the Potomac River across the Potomac Highlands into central Virginia. Temps in the 40s and 50s are expected Saturday on the cool side of the boundary but temps in the 60s and perhaps 70s are expected on the warm side of the boundary. Shortwave energy will also pass through the area...bringing the chances for showers. The best chance for rain will be along and north of the boundary where isentropic lift will add to the forcing. The boundary will likely remain nearly stationary Saturday night. Showers are possible with min temps ranging from the 40s north and east of the boundary to the 50s and perhaps lower 60s south of the boundary.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Low pressure will track northeastward across the upper Great Lakes on Sunday while its associated cold front is poised to move through our region the second half of Sunday. This will result in elevated rain chances and the potential for a few thunderstorms with the frontal passage as guidance indicates some instability/CAPE. 850 temperatures will start the day Sunday in the 11-13C range with WAA ongoing and we reside in the warm sector ahead of the cold front. These factors will help to deliver highs in the upper 60s or perhaps in to the 70s should the warmer guidance win out. As the front slides through the area by Sunday evening, and modest CAA takes over, 850 temperatures will have dropped off a good 10C and nearing 0C across our western zones. GFS/ECMWF differ in the progression of the front, as the ECMWF stalls the front to our southeast on Monday, allowing a wave of low pressure to ride northeastward along it. This would keep chance POPs at least for the southern half of our CWA into Monday, while the GFS keeps the front much further south, thus our region remains dry. Will maintain rain chances during the day on Monday for now and see if a little better agreement can be achieved. High pressure of Pacific origin moves in from the west and sets up shop over our region through Tuesday. Temperatures during this period will continue to remain above normal with highs in the mid to upper 50s, and overnight lows above freezing in the 30s/40s. The aforementioned high pressure shifts off the Carolina coast on Wednesday, delivering a return flow across the region. Global models then diverge once again on the strength and timing of a low pressure area moving northeastward out of the ArkLaTex region. GFS is faster and stronger, bringing increased rain chances by Wednesday night, while the ECMWF is slower and weaker, keeping much of the precipitation away from our area. For now, have introduced chance POPs Wednesday night for much of the area. Regardless, clouds will be on the increase Wednesday and Wednesday night as an upper level jet resides overhead and undulations in the mid-levels near our region. Temperatures will remain above normal Wednesday and Wednesday night with WAA and cloud cover favored. && .AVIATION /15Z THURSDAY THROUGH MONDAY/...
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A stalled front will linger just to our south the remainder of the day. Warm and moist air will overrun the surface cooler air in place...resulting in low clouds along with times of rain and drizzle through Friday night. IFR conditions are likely...but certainty as to when the IFR conditions begin is low. Thinking is IFR could begin in the early to middle hours of this afternoon. The boundary may lift a bit farther north Saturday and Saturday night. Most terminals should still be on the cool side of the boundary which means more low clouds along with areas of fog...light rain and drizzle. Perhaps KCHO will have improving conditions with the boundary setting up just to their north. A cold front will approach and cross the area on Sunday, moving east of the terminals by Sunday evening. This will result in increased rain chances, and perhaps a few thunderstorms, as MVFR/IFR VIS/CIGs look like a good bet. Winds will favor a southerly trajectory ahead of the front, veering out of the west northwest Sunday evening while conditions gradually improve overnight Sunday as drier air filters in to the region. High pressure will move in from the west through Monday night, providing dry weather, light winds and VFR conditions at all terminals.
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&& .MARINE...
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A stalled front just to our south will allow for persistent light north to northeast winds through the remainder of the day and into tonight. A Small Craft Advisory is in effect for Maryland Chesapeake Bay and lower Tidal Potomac River this afternoon through this evening. The boundary will likely remain to the south through Saturday night. As of now...it appears that the gradient will be light enough for winds to remain below SCA criteria. SCA conditions possible Sunday as a cold front approaches from the west and crosses our waters by Sunday evening. This front will bring increased rain chances and perhaps a few thunderstorms with its passage. High pressure of Pacific origin will build in from the west in the wake of the FROPA, delivering light winds over our waters, with no headlines expected through Monday night.
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&& .CLIMATE... From Wednesday February 21st the following records were broken. For IAD: A monthly record high minimum temperature of 59 degrees occurred. This breaks the old record of 55 degrees set on February 17th 1976. The high of 80 degrees was also a monthly record, breaking the old record of 79 degrees set on February 24th 1985 and February 25th 2000. For DCA: A daily record high minimum temperature of 56 degrees occurred. This breaks the old record of 51 degrees set in 1954. The high of 82 degrees was also a daily record, breaking the old record of 75 degrees set in 1953. For BWI: A daily record high minimum temperature of 52 degrees occurred. This breaks the old record of 49 degrees set in 1981. The high of 79 degrees was also a daily record, breaking the old record of 74 degrees set in 1930. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until midnight EST tonight for ANZ530>534- 537>543.
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&& $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...BKF AVIATION...BKF/KLW MARINE...BKF/KLW CLIMATE...

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